NEW YORK (AP) — New York City announced the closings of its mass transit and school systems, both the nation's largest, and ordered residents to leave some low-lying areas Sunday ahead of the massive storm approaching the eastern third of the U.S.

"You don't want to be overly panicked and overly prepared, but you want to be prudent, you want to do what's necessary," New York Gov. Andrew Cuomo said Sunday in announcing the suspension of the city's subways, buses and commuter trains. Cuomo had scheduled a news conference for later in the day in Kingston, but later cancelled it.

Rainfall is expected to start late Sunday or early Monday in New York. Hurricane Sandy was headed north from the Caribbean to meet both a snowstorm and a cold front, and experts said the rare hybrid storm that results will cause havoc over 800 miles from the East Coast to the Great Lakes. And one expert expressed concern about when the worst of the storm surge would hit: at high tide or at low.

Amtrak says it is canceling service across the northeastern U.S. on Monday as Hurricane Sandy threatens to create a wet, windy mess in the region. Amtrak said in a news release Sunday that it was canceling all service north of New York at 7 p.m. Nearly all service across the Eastern Seaboard will be canceled starting Monday. Amtrak says it has not yet determined when train services will resume. Alternate transportation is not available.

"This will be the crux," said Klaus Jacob, a Columbia University researcher who has advised the city on coastal risks. "If we have bad luck, then it arrives coinciding with high astronomical tides. ... If it arrives at the lower astronomical tides, then we will have lucked out."

A storm surge of 6 to 11 feet was expected, Mayor Michael Bloomberg said, and he ordered an evacuation of the low-lying areas along the edges of the city, including parts of lower Manhattan like Battery Park City and some of the financial district, sections of Brooklyn and Staten Island and the Rockaways in Queens.

"If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," he said at a news conference Sunday. "... This is a serious and dangerous storm."

But, he said, those who didn't leave wouldn't be arrested. Ralph Gorham, co-owner of the Red Hook Lobster Pound in Brooklyn's low-lying Red Hook neighborhood, was one of those planned to stay.

"When the bell tolls, you live with it," he said Sunday. He said he had planned ahead and kept from ordering his usual batch of live lobsters from Maine, to diminish possible financial losses.

Gorham also said he was going to the storefront lobster business, usually crowded on weekends with clients, to set up generators and cables to keep the refrigerators and freezers going if power goes out.

Broadway took the threat of the mammoth storm seriously, with theater owners canceling all Sunday evening and Monday performances of shows like "The Book of Mormon" ''Once" and "Mama Mia!" long before a drop of rain fell in Times Square.

"The safety and security of theatregoers and employees is everyone's primary concern," said Charlotte St. Martin, executive director of The Broadway League, which represents producers.

Forecasts called for rain late Sunday or early Monday, and subway and public transportation service is to be halted Sunday evening, potentially stranding theatergoers. Refunds will be made available from the point of purchase.

Off-Broadway shows including "Stomp," ''Bad Jews" and "Golden Child" were also canceled Sunday night. Most matinees on and off Broadway stayed open. Mondays are usually very light on Broadway, with most shows having that as their day off.

Some Broadway shows had no evening shows scheduled Sunday, including "Cyrano de Bergerac," ''Annie," ''Chaplin," ''Enemy of the People," ''Once," ''Jersey Boys" and "Nice Work If You Can Get It."If forecasts hold, and especially if the storm surge coincides with high tide, the effects should be much more severe for the city than those in Irene. While the storm may not be the worst-case scenario, Jacob said he expected the subway system, as well as underground electrical systems and neighborhoods in Lower Manhattan, to be at least partially flooded. Many other low-lying areas of the city also face possible inundation, including some industrial waterfront areas where chemicals are stored, he said.

"We have to prepare to the extent we can, but I'm afraid that from a subway point of view, I think it's beyond sheer preparations. I do not think that there's enough emergency measures that will help prevent the subway from flooding," he said Sunday by phone.

The suspension of the city's transit system was the second in two years. Service was also suspended during Tropical Storm Irene last year. With a daily ridership of more than 5 million, New York City's subway system is by far the largest in the U.S., and many New Yorkers do not have cars and depend on subways and buses to get to work, school and around town.

Cuomo said the transit system will be suspended starting at 7 p.m. Sunday, when the last subways and final Metro-North and Long Island Rail Road commuter trains would run. The last buses will run at 9 p.m. He said the decision to shut down the area's bridges and tunnels would be made on a case-by-case basis.

The city's school system, which serves 1.1 million students, will be closed Monday, Bloomberg said. Cuomo also said the National Guard would be deployed, 200 troops in New York City, and 400 on Long Island.

At Penn Station, Lori Wolfman, in town for a friend's wedding, waited in a long line to change her tickets. She and her husband were scheduled to leave at 3 p.m. to go home to Washington, where they recently moved from California. But when the noon wedding brunch was canceled and the hotel announced plans to evacuate, they were eager to catch an earlier train.

"We'll get on anything," she said.

"It says they're all sold out," said Barry Wolfman, just back from the Amtrak kiosk. "I don't know if you can just get on an earlier train?"

"No," Lori replied. "I think we're going to be here until 3."

They decided to wait in line just in case, with nothing else to do for about three hours.